Trace element analysis requirements

Biological matrices usually require sample preparation prior to trace element analysis. These sample preparations, such as acid digestion or extractions, are labour intensive and can benefit significantly from laboratory automation to reduce both time and manual manipulations. 

LA-ICP-MS is a very suitable analytical method for direct trace element analysis on a small area of thin pure foil, because no sample preparation is required. The results of the determination of noble metals in a thin difficult to dissolve rhodium foil measured by LA-ICP-MS are... 

The ICP-AES instruments may have different configurations with the torch, which may be positioned either horizontally (axial ICP) or vertically (radial ICP). Because of the longer sample residence time in the axial ICP torch, the axial ICP-AES instruments are more sensitive than the radial ones. The state-of-the-art axial ICP-AES instruments (also called the trace ICP) have the high sensitivity that is required for trace element analysis of drinking water. 

Different analytical methods used for the analysis of samples collected under the requirements of different environmental laws are discussed in Chapter 2.4. Although many of these methods target the same analytes, their calibration requirements are different. Tables 4.5, 4.6, and 4.7 summarize the differences in calibration requirements for organic compound and trace element analysis. (Inorganic analyte methods and techniques have a range of requirements that cannot be summarized in a concise manner we should refer to specific methods for this information). 

Table 4.7 Calibration requirements for trace element analysis methods...

One of the most challenging aspects of atomic spectrometry is the incredibly wide variety of sample types that require elemental analysis. Samples cover the gamut of solids, liquids, and gases. By the nature of most modem spectrochemical methods, the latter two states are much more readily presented to sources that operate at atmospheric pressure. The most widely used of these techniques are flame and graphite furnace atomic absorption spectrophotometry (FAAS and GF-AAS) [1,2] and inductively coupled plasma atomic emission and mass spectrometries (ICP-AES and MS) [3-5]. As described in other chapters of this volume, ICP-MS is the workhorse technique for the trace element analysis of samples in the solution phase—either those that are native liquids or solids that are subjected to some sort of dissolution procedure. 

Inductively coupled plasma emission spectrometry is a standard method for trace elemental analysis. While sensitive and selective, these instruments are large and require considerable support solutions... 

Advantages Let us assume for the moment that the requirements for most trace element analysis methods are also met here These are that a known amount of an enriched Isotope of the element In question (spike) has been added to the sample that subsequent chemical processing renders the spike and endogenous analyte In the same chemical form and that contamination Is under control The second assumption, equilibration of analyte and spike, can be a critical one. In that lack of equilibration could contribute systematic errors ... 

For these reasons, activation analysis is preferably applied for certification and calibration purposes in trace element analysis. On the other hand, activation analysis is seldom used as a routine method, because handling of radioactive samples and disposal of the radioctive waste require special precautions. 

Activation analysis is extremely sensitive and accurate, does not require a high degree of manipulative skill, and avoids many of the problems of contamination which often affect trace element analysis. At least 70 elements can be determined by this method, some in amounts as small as g, and its application to biological fluids is described by Leddicotte (L5). 

This discussion examines the recent progress of nutritional trace element research and its implications for trace element analysis. Elements recently identified as essential are present in low concentrations for which analytical methods are not yet reliable. Biological availability of trace elements depends on chemical form and on interactions with other inorganic and organic constituents of the diet. Therefore, information on elemental species is required, in addition to quantitative data. Finally, the demonstration of essential functions of trace elements previously known only for their toxicity necessitates establishing safe ranges of intake, free from danger of chronic toxicity but sufficient to meet human needs. 

The determination of small quantities of azide and the analysis of single crystals require sensitive but nonsubjective methods of analysis. This section discusses relevant methods of sample preparation and analysis as they relate to small samples the next section discusses techniques suitable for trace-element analysis. 

Uses. Trace elemental analysis methods are invariably based on techniques which require standards for recovery studies as well as quantitation. The use of aqueous inorganic standards to calibrate measurements of metals in mineralized petroleum samples is well established. Such standards, however, give no information about the fate of the analyte during the critical sample preparation step. Therefore organometal-lic standards are required for trace element recovery studies on petroleum, regardless of whether the analysis is carried out directly or after mineralization. 

Knight MJ (1980) A Comparison of Four Digestion Procedures not Requiring Perchloric Acid for the Trace-Element Analysis of Plant Material. Argonne National Laboratory, Report ANL/LRP-TM-18, pp. 1-27, Argonne, IL. 

Solid sampling techniques enable direct analysis of the homogenised tissues. A number of such applications for analysing solid biological tissues have been reported (Chakrabarti et al., 1980 Lundgren and Johansson, 1974, Nordahl, 1990). However the dried tissue invariably needs to be solubilised for trace element analysis using techniques requiring the sample in a solution form (Fry and Denton, 1977 Hohl et al., 1989). 

The ultimate goal for any trace element analysis of sea water is to determine the amount and chemical activities of the element associated with the diflFerent forms in which it may exist. The development of a procedure for such an analysis requires both a thorough knowledge of the physico-chemical behaviour of the element in question and methods capable of fractionating a sample. Presently, we have not the necessary knowledge of the chemistry of the lanthanides in sea water. In addition, the present state of the art of fractionation of sea water samples prohibits the development of such procedures as mentioned above. 

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